Tomato plants of the species Solanum lycopersicum belong to the nightshade family, also known as Solanaceae. Within this family it is nowadays grouped in the genus Solanum, which does not only harbor tomato, but also the important food crops potato and eggplant. It is a perennial, herbaceous, flowering plant species which is native to South America.
Other species that are related to tomato within the Solanum genus are Solanum pimpinellifolium, Solanum chilense, Solanum peruvianum and Solanum habrochaites. Although it is known that crossing can be considerably difficult, these species are used to obtain traits that are valuable in growing tomato. In the recent history, advancement in tomato breeding has lead to tomato varieties having, for example higher yield, higher disease resistance and increased shelf life.
Tomato plants are being cultivated worldwide for their highly nutritious fruits. The tomato fruit is consumed in various ways, including raw, as an ingredient in many dishes and sauces, and in drinks. While it is botanically a fruit, it is considered a vegetable for culinary purposes. The fruit is rich in lycopene, which may have beneficial health effects. In 2009, the total acreage for both fresh and processing tomatoes in the United States was approximately 442,100 acres, with a total production of about 14,141,920 tons (source: USDA).
Commercial vegetable production, including the production of tomato, is affected by many conditions. The choice of the grower for a certain variety is a determining factor, and forms the genetic basis for the result that can be attained. In addition, there are many external factors that influence the outcome. Growing conditions like climate, soil, and the use of inputs like fertilizer play a major role. There are various ways of cultivating tomatoes, among which, the most common are: open field, greenhouse and shade house production. Although the species can be grown under a wide range of climatic conditions, it performs most successfully under dry and warm conditions. In addition to this, the presence of pests and diseases also affects the total yield that can be reached.
In order to create tomato varieties that are satisfying the needs of growers and/or consumers, many considerations have to be taken into account. The goal is to combine within a single variety or hybrid an improved combination of desirable traits from the parental germplasms. These traits may include higher yield, field performance, fruit and agronomic quality such as firmness, color, content in soluble solids, acidity and viscosity, resistance to diseases and insects, and tolerance to drought and heat. With mechanical harvesting of the tomato fruits for processing purpose, i.e., juice, paste, catsup, etc., uniformity of plant characteristics such as germination, growth rate, maturity, and plant uniformity is also important.
Tomato is a simple diploid species with twelve pairs of chromosomes. The cultivated tomato is self-fertile and almost exclusively self-pollinating. The tomato flowers are hermaphrodites. Tomato cultivars were initially open-pollinated, such as many well-known heirloom tomatoes, but also varieties were developed for large scale growing facilities. Nowadays, especially in a professional growing setting these cultivars are replaced by better yielding hybrids. Due to its wide dissemination and high value, tomato has been intensively bred. This explains why such a wide array of tomatoes are now available. The size may range from small to large, and there are cherry, plum, pear, standard, and beefsteak types. Tomatoes may be grouped by the amount of time it takes for the plants to mature fruit for harvest; in general the cultivars are considered to be early, midseason or late-maturing. Tomatoes can also be grouped by the plant's growing habit, being determinate or indeterminate. Determinate plants tend to grow their foliage first, then set flowers that mature into fruit if pollination is successful. All of the fruit tend to ripen on a plant at about the same time. Indeterminate tomatoes start out by growing some foliage, then continue to produce foliage and flowers throughout the growing season. These plants will tend to have tomato fruit in different stages of maturity at any given time. More recent developments in tomato breeding have led to a wider array of fruit color. In addition to the standard red ripe color, tomatoes can be creamy white, lime green, pink, yellow, golden, or orange.
Also breeding for multiple disease and pest resistances is an important aspect in providing varieties for multiple growing systems and climates. These diseases can be the result of attacks of either nematodes, bacteria, fungi, viruses and/or insects. Important micro-organisms causing such diseases in tomato plants and their fruits in this respect include: Meloidogyne incognita (Mi), Verticillium dahliae race 0 (Vd), Fusarium oxysporum f. sp. lycopersici race 0 (exl) and race 1 (ex2) (Fol), Fusarium oxysporum f. sp. radicis lycopersici (For), Cladosporium fulvum groups A, B, C, D and E (Ff), Tomato Mosaic Virus (ToMV) strain 0, 1 and 2, Stemphylium spp., Tomato Spotted Wilt Virus (TSWV) and Oidium neolycopersici (On).
The way in which fruits from tomato plants are harvested is also relevant. When the fruits are not ripe at the same time, single harvest of fruits has to be applied in order to provide a fresh product to the consumer. In the case that fruits of one truss are ripening synchronous, the whole truss can be harvested and be marketed. To support this development, the interest for breeding of uniform ripening trusses has increased in the recent years.
Oidium neolycopersici is the causal agent of powdery mildew disease in tomato. The lack of a sexual stage hampers the exact identification of this pathogen, but it is believed to belong to the Ascomycetes. The fungus causes powdery white lesions on the adaxial tomato leaf surface and might also infect other abaxial surfaces, the petioles and the calyx. The tomato fruit generally remains uninfected. Severe infection of a tomato plant might result in premature senescence, leaf chlorosis and a marked reduction of the tomato fruit size. (Jones et al. Mol. Plant Pathol. 2(6), 303-309, 2001)
Silvering in tomato, also known as ‘chimera’ is a disorder that is not related to a disease caused by bacteria, viruses, insects or a combination thereof. It is called ‘head silvering’ when it affects the leaves that are formed in the shoot apical meristem of tomato plants. This disorder primarily affects tomato that is grown in protected conditions, especially in northern latitude areas of production. The white or silver color in the tissues of the leaves is caused by large intracellular spaces which develop through an abnormal formation of palisade tissue of the leaf. This happens at a very early stage of development. The main factor to positively and negatively influence this phenomenon is a drastic decrease of temperature, especially at the level of the shoot apical meristem. Silvering thus affects general plant condition but might also result in deformed fruits, optionally showing greenish to yellow streaks (Blancard et al. in Tomato Diseases: Identification, Biology and Control, Manson Publishing, 2012).
Citation or identification of any document in this application is not an admission that such document is available as prior art to the present invention.